A new method of doping pyrolytic graphite utilizing laser heating in the presence of organic heteroatomic vapors

When pyrolytic graphite is heated with a high-energy pulsed Nd:YAG laser in the presence of pyrrole or 3-methylthiophene vapors, the surface becomes doped with nitrogen or sulfur, respectively. The time frame of the intense heating is such that the lattice does not undergo any extensive rearrangement, and the methodology results in modification of the properties of the graphite by introducing donor or acceptor atoms into the array. The doped graphites are analyzed by X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), X-ray diffraction (XRD), X-ray fluorescence microscopy (XFM), and/or scanning electron microscopy (SEM). XPS indicates chemical shifts in the carbon 1s energies for the nitrogen and sulfur doped samples. AES shows changes in the carbon KLL emission energies upon doping. Correlation of these shifts with the XRD allows definition of the chemical bonding present. Nitrogen is covalently bound to carbon at the domain edges and at trigonal sites, breaking the local aromaticity of the lattice. Sulfur, on the other hand, is interstitially located, resulting in a small lattice expansion along the c-axis of similar to 0.01 Angstrom, and is easily removed by Ar ion sputtering.